The conventional apparatus used in the recovery of silver from photographic film usually comprise a wash tank, a centrifuge and a rinse tank. After each cycle, the wash and rinse waters are discarded.
Known methods of recovering silver make use of a proteolytic enzyme or in the alternative a weak caustic solution.
For example, Canadian patent No. 983,722 discloses a method for recovering silver comprising the steps of mixing the wash water with an endopeptidase while maintaining the pH of the wash water alkaline, thereby breaking down the gelatin molecules to soluble peptide units, acidifying the wash water to effect the precipitation of the silver and separating the silver from the supernatant liquid.
U.S. Pat. No. 3,647,422 discloses a process which comprises subjecting the photographic film to a caustic solution maintained at an elevated temperature which results in the separation of the film constituents from the film base. The latter are recovered by filtration.
An object of the present invention is to provide a method which allows for a higher recovery of the silver from the film.
A further object is to provide a closed circulation system for the recovery of silver.